Component lifing is a process of determining an estimated operational lifetime of a component. In the aviation industry, lifing of engine components is crucial to integrity and mission safety. Various certification bodies certify approved lifetimes of engine components after which there is an unacceptable probability of component failure (e.g. through material fatigue or material anomaly) and there is the requirement that the engine component is repaired or replaced at or before the end of the approved lifetime. Other industries also analyse operational lifetimes by component lifing.
The approved lifetime of engine components is typically calculated from a finite element analysis (FEA) of the stresses and temperatures experienced by the engine component during a theoretical certification mission.
In the FEA of the engine component, a model of the component is divided into a number of finite elements, each of which has nodes with defined material properties so that any applied load will give a predictable corresponding displacement of the element. Complex designs are made up as an assembly of elements, called a mesh, to which restraints/constraints and loads may be applied. During the FEA, a series of simultaneous equations are set up which represent the overall mechanical behaviour of the model, and these are solved, giving the nodal displacements resulting from the applied loads.
Rig tests on actual engine components are then used to validate the theoretical prediction obtained from the FEA.
One problem with the known methods/systems is that the theoretical operating conditions attributed to the certification mission may differ considerably from the actual operating conditions experienced by the part in service. Where the actual operating conditions are harsher than the theoretical operating conditions, failure of the part may occur earlier than predicted which could have catastrophic effects. Where the actual operating conditions are less harsh than the theoretical operating conditions, the part may be replaced sooner than is necessary with undesirable financial implications for the operator.
Another problem is that the methods/systems are time-consuming. As a consequence, typically, the FEA is carried out for one or two certification missions, but is too slow to be used with actual in service data.